The invention relates to a slitter-winder for winding of pulp webs, and more particularly to a slitter-winder for winding of pulp webs and corresponding thick webs having two drums for supporting at least two web rolls.
The pulp web is made in a cellulose drying production line, wherein the production line comprises the cellulose drying machine and equipment for performing further treatment on the dried cellulose web. Density of the pulp web is about 400-800 kg/m3 and thickness of the pulp web is about 0.5-2.5 mm.
In manufacturing lines known from the prior art pulp web making takes place as a continuous process. A pulp web completing in a machine is wound with a reel-up around a reeling shaft, i.e. reel spool, into a machine roll (a parent roll). The purpose of reeling is to modify the web manufactured as planar into a more easily processable form. In the reel-up the continuous process of the machine breaks for the first time and shifts into periodic operation. This periodicity is tried to be made as efficiently as possible in order to avoid waste of already completed work in earlier process stages.
The pulp web wound onto the machine roll is full-width so it must be slit into partial webs with a suitable width. The partial webs are wound to partial web rolls (customer rolls) of suitable length or of suitable diameter for the customers. The slitting and winding take place as known from the prior art in an appropriate separate machine, i.e. in a slitter-winder.
As known from the prior art, in the slitter-winder the machine roll is unwound, and the wide web is slit on the slitting section into several narrower partial webs which are wound up on the winding section around winding cores or around winding shafts or around winding cores located on the shafts, such as spools, into customer rolls. When the customer rolls are completed, the slitter-winder is stopped and the rolls, i.e. the so-called set, is removed from the machine after which the process is continued with the winding of a new set. These stages are repeated periodically until the web runs out of the machine roll, at which point a machine roll change is performed and the operation starts again as the unwinding of a new machine roll. When producing customer rolls of pulp web grades a set of customer rolls of desired diameter is rapidly formed. Once the customer rolls are formed new winding cores/a new winding shaft with or without winding cores must be placed in the winder for the beginning of winding of the next set of customer rolls and the end of each partial pulp web must be lead and attached to the winding core.
Slitter-winders employ winding devices of different types, for example winders and two-drum winders. In the two-drum winders the partial webs are wound around winding cores supported by two winding drums to partial web rolls via a nip between the winding drums and the partial pulp web rolls being formed. In the two-drum winders also a belt arrangement i.e. a so-called set of belt rolls with belt loop or belt loops located around two guide rolls can be used as the winding drum. As known in the prior art, winding with a shaft without cores or together with cores can be employed in the winding of a pulp web into customer rolls on a slitter-winder.
The present invention relates to two drum winders with two winding drums.
Typically in winding of pulp webs only two-drum winders have been used. In the winder the winding drums have been hard roll shells of steel or cast iron and in some cases with a thin hard coating of carbides, typically of tungsten carbides.
One problem that exists when a pulp web is wound with a two-drum winder is that the winding nip formed between the pulp web roll and the winding drums does not function well at the beginning of the winding. The non-functioning winding nip means on the one hand that the tail of the web is difficult to thread into the winding nip and on the other hand that the nip pressure does not provide enough traction to the pulp web and thus the winding of especially the first layers is non-uniform and leads to poor winding on the bottom of the roll. This is partly caused by the fact that use of a heavy rider roll load, which would help the functioning of the winding at the beginning, is not possible, since a heavy rider roll load would easily lead to breaks in the pulp web. Neither is web tension a proper winding parameter in winding of pulp webs, since high tension values are needed in order to stretch the pulp web, but too high web tension easily breaks the pulp web, which typically is not homogeneous. The high tension may also cause sliding of the pulp roll in the winding nip against the winding drums.
Due to the drying process of the pulp the pulp web is not homogenous and in pulp winders some of the partial webs remain loose, in particular at the beginning of the winding due to the reason that it is not possible to stretch the non-homogenous partial pulp webs sufficiently by the available web tension in order to achieve sufficient tension in all partial pulp webs.
Furthermore, the nip induced addition to the web tension is negligible, since the pulp roll is in the beginning too hard due to the hard core or shaft to allow the nip induced mechanism to work. After several layers have been wound around the winding shaft or core the nip induced tension mechanism starts to work as the pulp rolls become capable of deforming substantially in the radial direction. Finally all the partial webs reach a sufficient level of web tension, since the nip induced tension becomes higher for the pulp rolls corresponding to looser partial webs due to the larger radial deformations of these softer rolls.
Due to the non-homogenous web and the non-functioning winding nip at the near beginning of the winding the bottom of the wound roll tends to be loose, which easily leads to shifted layers in the wound pulp roll. In the worst cases there happens a phenomenon called nip rejection, where a loose bag in the pulp web forms in front of the nip. The nip rejection usually leads to a pulp web break.
The prior art of slitter-winders for paper and board winding includes winding drums having elastomeric covers. Earlier the practice was to construct these covers with a hardness of 85 Shore “A” (ShA), or greater, but nowadays also covers with a hardness as soft as 65 Shore “A” (ShA) are used. On the Shore “A” (ShA) scale, readings approaching 100 are relatively hard, and readings approaching 25 are relatively soft. If the elastomeric cover is made quite hard, such as having a hardness of about 95 Shore “A” (ShA), or harder, then its operational characteristics are relatively similar to those of a steel drum. That is, the nip area is quite narrow, even approaching line contact, which provides neither a relatively large, nor soft, nip contact.
In U.S. Pat. No. 7,458,539 is described a winder roll starting apparatus for thick webs. In US patent application publication 2012/0091248 is described a method and apparatus for threading a fibrous material web in a winder. These prior art publications relate thus to the problem of threading of the web and not to the problems of beginning of winding i.e. to the winding of a few first layers of the pulp web after the pulp web has been threaded nor to the problems of functioning of the winding nip during winding of the early layers of the pulp web.
It is known from slitter-winders for paper or board winding to use as a winding drum a roll with soft cover. For example in EP patent publication 0679595 is disclosed a winding roll with an elastomeric cover which has a hardness between 65 and 80 Shore A, for increasing production speed and providing careful winding such that surface faults of the paper or board web or winding faults of the paper or board roll to be wound are avoided. In EP patent publication 0879199 is disclosed a roll for a winder with a deformable layer with the compression modulus less than 10 MPa for providing winding without winding faults in the wound paper of the board roll. In U.S. Pat. No. 6,234,419 is disclosed a winding-up process and machine for winding paper or board webs in which a winding roll with a volume compressible outer layer with a compression modulus lower than 10 MPa for winding of fiber webs that have grammage of less g/m2 with high quality and high speed. In U.S. Pat. No. 5,553,806 is disclosed a support or rider roll for a paper roll winder in which the roll has an outer elastomeric cover with pattern, open to surface arranged such that the effective hardness of the cover ranges between 30 and 55 Shore A for providing a softer and wider nip with a long service life. In addition, in U.S. Pat. No. 5,575,436 is disclosed a winder for webs in which a drum with a covering layer with an outer surface pattern providing a series of recesses and land areas is provided for high speed winding to reduce noise and to reduce winding nip induced tension. The prior art relating to winders for paper or board, in which a winding roll with a soft cover is used, does not teach anything relating to the above discussed problems at the beginning of winding of pulp webs in a slitter winder nor do they give any hint to solving the above discussed problems as these problems are due to the characteristics of pulp webs, which are typically much more non-homogenous than paper or board webs, and these problems do not occur in paper or board winding.